Higher values of fluctuating asymmetry (FA), differences between traits on the left and right sides of an organism, have been associated with a wide range of medical conditions, presumably because high FA represents non-optimal organismal development. Detailed studies of FA, however, have failed to unambiguously demonstrate a genetic basis of FA. This study will use artificial selection and independent developmental stability assays to test whether FA measurements accurately represent a global property of developmental stability. Drosophila lines will be selected for higher or lower levels of FA, changes that should alter the developmental stability of the flies if FA has a genetic basis and truly represents overall developmental stability. These lines will then be tested with a series of independent assays of developmental stability, directly testing for the existence of a single developmental stability trait associated with FA. The results from this study will have important ramifications for the medical community because the use of FA to investigate medical conditions is increasing. Providing or withdrawing support for the use of FA will guide researchers in their effort to understand what social or medical factors are associated with a variety of developmental errors. Additionally, the data gathered from this study will address a deeper conceptual issue in developmental genetics, whether there is such a trait as a global stability property.